The present invention relates to well bore stabilization and, more particularly, to treatment fluids that may reduce the tendency of shales to swell and associated methods.
A treatment fluid may be used in a subterranean formation in a variety of ways. For example, a fluid may be used to drill a well bore in a subterranean formation, to stimulate a well bore in a subterranean formation, or to complete a well bore in a subterranean formation, as well as or for a number of other purposes. The process of drilling a well typically requires the use of a drilling fluid. A drilling fluid used in connection with drilling a well in a subterranean formation may comprise a number of fluids (gaseous or liquid) and mixtures of fluids and solids (e.g., as solid suspensions, mixtures and/or emulsions of liquids, gases and solids) used in operations to drill well bores into subterranean formations. Drilling fluids are used, inter alia, to cool the drill bit, to lubricate the rotating drill pipe to prevent it from sticking to the walls of the well bore, to prevent blowouts by serving as a hydrostatic head to counteract the sudden entrance into the well bore of high pressure formation fluids, and to remove drill cuttings from the well bore.
During the drilling of subterranean well bores, it is not uncommon to encounter strata comprising shales. As referred to herein, the term “shale” will be understood to mean materials such as certain types of clays (e.g., bentonite) and related subterranean materials that may “swell,” or increase in volume, when exposed to water. The shale may be problematic during drilling operations because, inter alia, of its tendency to swell when exposed to aqueous media, such as aqueous-based drilling fluids. Shale swelling may result in undesirable drilling conditions and undesirable interference with the drilling fluid. The increase in bulk volume of the shale associated with shale swelling may impede the removal of drill cuttings from beneath the drill bit, increase the friction between the drill string and the sides of the well bore, and inhibit the formation of a desirable filter cake on the formation. Shale swelling also may result in other problems, such as the loss of drilling fluid circulation or stuck pipe that may result in undesirable delays and expenses. Furthermore, shale swelling also may substantially decrease the stability of the well bore, which may cause irregularities in the diameter of the well bore, e.g., the diameter of some portions of the well bore may be either smaller or greater than optimally desired. In an extreme case, shale swelling may decrease the stability of the well bore to such an extent that the well bore may collapse.
A traditional method of inhibiting shale degradation during drilling has been to use an oil-based drilling fluid as opposed to an aqueous-based drilling fluid. However, environmental regulations enacted by numerous countries have limited the use of oil-based drilling fluids. Other attempts to counteract the problems associated with shale degradation during drilling have been to include shale-inhibiting components in an aqueous-based drilling fluid. As used herein, a “shale-inhibiting component” refers to a compound that demonstrates a propensity for inhibiting the tendency of shales to swell by absorbing water. Salts, such as potassium chloride, are one example of a conventional shale-inhibiting component. While salts may reduce the tendency of shales to swell, they also may flocculate the shale, resulting in undesirable fluid loss and a loss of thixotropy. Furthermore, an increase in salinity may result in a decrease in the functional characteristics of drilling fluid additives. Other examples of conventional shale-inhibiting components include, but are not limited to, amphoteric materials, polyglycols, partially hydrolyzed polyacrylamides, combinations of thickeners such as a copolymer and a polysaccharide, and polymers with a hydrophilic group and a hydrophobic group. However, these conventional shale-inhibiting components may not provide a desired level of shale swelling inhibition and/or may be environmentally undesirable in certain regions of the world.